Cleanups for release 2.4

Marian Piatkowskirequested to merge
cleanup/release-2.4 into master

This branch contains major updates, in particular

  • switch to CMake as a default build system
  • add CMake tests for HDF5 and FFTW3
  • update (almost) everything to version 2.4 of core modules and dune-pdelab

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